1. Field of the Invention
The present invention relates to a controller for an electric vehicle and an electric vehicle using the same, and more particularly, relates to a control technology for a generator-driving engine in a series hybrid electric vehicle, where electric power to be supplied to a battery which supplies its electric power to a vehicle-driving electric motor is supplied by a generator driven by utilizing a generator-driving engine (for example, a generator-driving internal combustion engine).
2. Description of the Related Art
There has so far been an electric vehicle called a series hybrid electric vehicle (SHEV) as the electric vehicle provided with a generator and a generator-driving engine.
Such a SHEV has been developed with a view to securing a longer driving distance of an electric vehicle (EV) by utilizing electric power generated by a generator.
More specifically, there has been a conventional method for controlling a generator in the following manner.
When the battery is in a status of being sufficiently charged with electric power, the electric vehicle is driven by use of only energy supplied by the battery, and when the battery comes to a status of being not sufficiently charged with electric power, a generator-driving engine is started and a power generation by the generator is started.
Then, energy obtained by this power generation is used for charging the battery and/or as energy for operating a driving motor. When the battery reaches a sufficiently charged status, the generator-driving engine is stopped and the power generation by the generator is finished.
Generally a charging status of the battery is evaluated by using a "state of charge (SOC)". More specifically, if the SOC is at or above a preset value, it is evaluated that the battery is in a sufficiently charged status and if the SOC is less than the preset value, it is evaluated that the battery is not in a sufficiently charged status.
For further details, a method for detecting the SOC by measuring a battery voltage under the condition that an accelerator position is at or below a predetermined value in order to accurately detect the SOC is disclosed in Japanese Patent Application Laid-open Publication No. 6-245324.
According to the conventional method, however, there has been such a case, for example, where a generator-driving engine is started when a vehicle is in a stopped status, because its generator starting timing or its timing for starting the generator-driving engine is determined based on only the SOC.
In such a case, there is a possibility that vibration and noise are generated by a cranking of the engine and the vibration and noise give uncomfortable feeling to the crew such as a driver and/or a passenger, that is, particularly decrease the feeling of quiet and smooth driving which is the characteristic of the electric vehicle.